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A217217
Dimension of totally primitive elements of the algebra "Baxter" of order n.
0
0, 1, 0, 1, 4, 19, 96, 511, 2832, 16215, 95374, 573837, 3520228, 21961119, 139038824, 891817687, 5787091552, 37946582995, 251173847170, 1676831257693, 11282156358500, 76453813499219, 521508969157826, 3578990500062417, 24700214881378152, 171359711873508367
OFFSET
0,5
REFERENCES
S. Giraudo, Algebraic and combinatorial structures on pairs of twin binary trees, Journal of Algebra, Volume 360, 15 June 2012, Pages 115-157.
LINKS
S. Giraudo, Algebraic and combinatorial structures on Baxter permutations, DMTCS proc. AO, FPSAC 2011 Rykjavik, (2011) 387-398.
FORMULA
Giraudo gives a generating function.
PROG
(PARI)
baxter(n) = sum(k=1, n, binomial(n+1, k-1) * binomial(n+1, k) * binomial(n+1, k+1) / (binomial(n+1, 1) * binomial(n+1, 2)));
lista(m) = {u = t + t*O(t^m); b = 1 + sum(n=1, m, baxter(n)*u^n); gfbt = (b-1)/b^2; for (n=0, m, print1(polcoeff(gfbt, n, t), ", ")); }
\\ Michel Marcus, Feb 16 2013
CROSSREFS
Cf. A001181.
Sequence in context: A122394 A047781 A089354 * A083315 A301417 A025573
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Oct 03 2012
EXTENSIONS
More terms from Michel Marcus, Feb 16 2013
STATUS
approved